The field of frame-based and so-called xe2x80x9cframelessxe2x80x9d stereotaxy is now developing and becoming adopted in the neurosurgical as well as other surgical contexts. In the case of frame-based stereotaxy, a frame is attached to the patient""s body, which does or can include a localizer structure such that when tomographic scanning is done with either CT or MRI imaging, fiducial points from the localizer appear on the tomographic slices to index the tomographic images into stereotactic coordinates. In the case of xe2x80x9cframelessxe2x80x9d stereotaxy, it is desired to not put a frame on the patient prior to tomographic imaging. One of the methods to index the scanner coordinate space to the actual patient physical coordinate space in the operating room is to place index markers either into the patient""s bony anatomy, such as the skull, or onto the external anatomy of the patient, such as skin staples or radiopaque marker dots on the patient""s skin.
The use of such index markers is illustrated in FIG. 1. Here the patient""s head 1 is resting on an external apparatus, in this case a reference plate 6. There are shown several methodologies for frameless stereotactic indexing or localizing. In the first, a mechanical articulated arm consisting of links 3, 4, and 5 with encoded joints between is attached to platform 6. Electronic information from the encoders of the arm is sent via cable 7 to a computer workstation 8. Such an arm can be calibrated to the patient""s anatomy 1 by touching off of discrete index points attached to the anatomy, such as markers 2A, 2B, 2C, and 2D. In principle, three non-co-linear index markers could reference the arm by a calibration maneuver to the physical space of the patient""s anatomy. This is now being done commonly with mechanical space pointers, and is described in the article by Drs. Guthrie and Adler. The index markers 2A, 2B, 2C, and 2D can be identifiable in tomographic image data taken of the patient""s head. That is, the markers may be radiopaque and thus appear in various CT slices. Similarly, the markers could have MRI medium in their composition so that they would be visible on MRI scanning. No such combined index markers have been reported in the literature. Index markers that could be used both for CT and MRI or other imaging would be highly utilitarian, as it would enable registration of multi-modal images and also would enable, with the self-same localizer, physical indexing from a mechanical index arm, such as that shown in FIG. 1.
Many other types of stereotactic localizers are now being reported at conferences and in the literature. For example, also shown in FIG. 1 is an electromagnetic device in which senders or receivers 12A, 12B, and 12C shown in phantom communicate with a sender or receive 11, which is attached to the stereotactic pointer 3. By appropriate triangulation or other spatial indexing, the senders and receivers on the base plate 6 can xe2x80x9cknowxe2x80x9d the position and orientation of the element 11, and thus the space pointer.
Yet another means for frameless localization would be by ultrasonic, sonic, optical, or other transducer means, which could be represented as elements 10A and 10B (shown in phontom) located in the field of the patient, and being received by elements 9A and 9B (shown in phontom) on the probe 3 so as to determine the probe""s position and orientation. Several schemes using sonic time of flight sparkers and passive or active optical slices would fall into this category.
The present invention relates to the design and construction of the index markers, such as those illustrated by 2A, 2B, 2C, and 2D in FIG. 1. An objective of the present invention would have these markers be compatible, both to CT, MR, and other localization methods such as P.E.T. scanning or angiography. Yet another objective of the present invention is that these markers would be so constructed that setting the space pointer 3 onto them in a surgical context would enable that the point end of probe 3 could be stably positioned on the marker during the calibration process. For example, if the heads were sterile draped for neurosurgery, one would wish to have the ability through the sterile drape to set the tip of probe 3 onto a marker for a short period of time during marker calibration process. Several embodiments of the present invention described below show how these objectives can be met.